SIMULATION OF ALBEDO AT A LANDSCAPE SCALE WITH THE D.A.R.T. MODEL AN EFFICIENT TOOL FOR EVALUATING COARSE SCALE SATELLITE PRODUCTS? Sylvie DUTHOIT*, Valrie DEMAREZ* Jean-Philippe GASTELLU-ETCHEGORRY*, Emmanuel MARTIN* Jean-Louis ROUJEAN** * CESBIO, ** Mto-France Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Field measurements over an agricultural area High resolution imagery (SPOT HRV data) DART tool simulations of remote sensing images Measurements over a long time period with good spatial sampling + Simulations of remote sensing images with DART Spatial and temporal dynamic of the BRDF and albedo Methodology The DART model The study area Input DART parameters Land cover map LAI Soils optical properties Leaves optical properties Landscape simulations Results Conclusions Main prospects Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Outline The D.A.R.T model Discrete Anisotropic Radiative Transfer (Gastellu et al., 1996; 2005) Principe Ray tracing method Discrete ordinate technique (space and directions) Matrix of parallelepipedic cells With/without atmosphere, topography Products Reflectance and temperature products (directional images) Radiative budget products (incident, intercepted, absorbed, scattered radiation for each scene level) Atmospheric products Sylvie DUTHOITWorkshop on Albedo Products, April 2005 THE DART model Opaque cells Soil, water surfaces, urban elements, trunks surface scattering Plane opaque surfaces: parametric reflectance models Sylvie DUTHOITWorkshop on Albedo Products, April 2005 DART images, nadir view (green, red & NIR spectral bands) Turbid cells Vegetation, air volume scattering LAD LAI THE DART model DART - Landscape release Optical and structural parameters Leaves 1: LAI 1, LAD 1, 1, 1 Leaves 2: LAI 2, LAD 2, 2, 2 Leaves 3: LAI 3, LAD 3, 3, 3 soil Land cover map Plots mosac Each plot is homogeneous (randomly distributed leaves) Sylvie DUTHOITWorkshop on Albedo Products, April 2005 THE DART model An agricultural study area : Lamasqure Sylvie DUTHOITWorkshop on Albedo Products, April 2005 The study area 6x6 km and 3x3 km For the study area, DART need: Land cover map of the area Mean PAI of each stand Informations about canopy structure Leaves optical properties Soils optical properties Sylvie DUTHOITWorkshop on Albedo Products, April 2005 The study area Land cover map Sylvie DUTHOITWorkshop on Albedo Products, April 2005 SPOT 2004 images Land cover map (Gouaux, Ducrot, CESBIO) DART input parameter Input DART parameters Wheat Corn Soya Sunflower Destructive PAI measurements Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Input DART parameters Seasonal evolution of the PAI Grassland = SMOSRex measurements (KerrY., CESBIO) Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Input DART parameters Spatialisation of the LAI Vegetation index/LAI relation SPOT images - corrected from atmospherical effects (SMAC model). - inter-calibrated (G. Dedieu, CESBIO) Sylvie DUTHOITWorkshop on Albedo Products, April PAI Input DART parameters 2 major types of soils on the area (INRA database) Soils optical properties Terreforts Boulbnes Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Measurements on plowed, sowed, dry and wet bare soils Input DART parameters Soils BRDF measurements Spectroradiometer ASD Directional measurements in several view angles Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Hapke model to simulate the bi-directionnal reflectance > parameters in the DART model Input DART parameters Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Leaves optical properties ASTER database Input DART parameters April 21, May 16 and July 17 Illuminations configurations for the time (date and hour) of the images 3 spectral bands ( , and m) diffuse radiation 20% LANDSCAPE SIMULATIONS Comparisons with SPOT reflectances Sylvie DUTHOITWorkshop on Albedo Products, April 2005 SPOT reflectance Landscape simulations FIRST RESULTS Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Comparisons SPOT/DART values Dry soils Landscape simulations Sylvie DUTHOITWorkshop on Albedo Products, April 2005 Comparisons SPOT/DART values Dry soils and wet soils Dry soils Wet soils Landscape simulations CONCLUSIONS Sylvie DUTHOITWorkshop on Albedo Products, April 2005 BUT the difference between simulations and SPOT reflectance values are not negligible: 1- soils optical properties for wet soils (rain, irrigation in july) measurements in progress on the area 2- leaves optical properties : different for each crop species AND seasonnal evolution PROSPECT simulations Results are encouraging The seasonnal evolution is well reproduced, in general PROSPECTS Stand scale validation - Directionnal reflectance measurements over crops canopies (ASD instrument) - Albedo measurements (K&Z net radiometer) over 2 crops stands Landscape scale simulations - Comparison with SPOT 3x3 km and 6x6 km. - Comparison with MODIS products: Black-sky albedo (16 days), Nadir- adjusted reflectance. Sylvie DUTHOITWorkshop on Albedo Products, April 2005 DART: professional release (CNES, 2005), freely available for scientists - Follow up of the work with new simulations for Comparison with SEVIRI products - Evaluation in the framework of the SAF-Land project. Sylvie DUTHOITWorkshop on Albedo Products, April 2005 THANK YOU ! Sylvie DUTHOITWorkshop on Albedo Products, April 2005 MODIS Black-sky albedo